Hi Robert,
I would appreciate others having a look at Roland's implementation as well.
I took a look at Rolands code some time ago as I built my own simple
shader composition for myself as well. The problems, I found myself with
shader composition is that I often need to customize the shaders. Many
people may want to keep functionality similar to OpenGL pipeline, thus
they would prefer to use Gouraud shading. Me, I want to use Phong
shading. One person may prefer Blinn-Phong (half-vector) specular
reflection, while I prefer Phong reflection (reflection vector). Some
people would want to include Shadow maps that needs their small piece of
code in fragment shader. Others as me, look for shadow volumes in the
future while they considers using geometry shaders.
In my opinion, the most difficult part of the design would be to allow a
programmer to make all these things and to add even more of them in the
future, based on the craziest (but meaningful) ideas of the programmers.
One more experience from me: Shader compilation is time expensive work
by my experience. Say, it is a real difference to compile twenty shaders
or compile one and reuse it twenty times from cache. It would be nice to
have a cache and if the shader of particular parameters were already
generated, it would be reused. (Not sure, if Rolands submission includes
cache feature.)
Looking forward to have a shader composition in OSG!
John
BTW: Sending copy to OSG-discussion as well, for others input.
Robert Osfield wrote:
In terms of the final approach I merge, I would like to retain the
flexibility of the OSG current StateAttribute + GL mode approach, this
is already a form of state composition that has all the
inheritance/compositional behavior that I'd like to see, but we
currently rely upon the GL drivers to do the mapping fixed function
pipeline to shaders for us. Roland's approach does provide something
similar to this, am I'm still learning about the implementation
details so can't yet comment in full of how close it gets.
I would appreciate others having a look at Roland's implementation as well.
Robert.
On Tue, Jun 22, 2010 at 12:56 PM, Wojciech Lewandowski
<lewandow...@ai.com.pl> wrote:
Hi, Robert
I hope you will also look at Virtual Program in shader composition example.
I am not trying to sell the implementation but I really would like to see
shader composition simple and easy to use and I think that VirtualProgram
approach could be seen as such fairly simple interface.
I was hoping that current osg::Program could be extended to allow incomplete
shaders like VirtualProgram allows. In that case VirtualProgram could be
removed. OSG could solve shader completness in similar way as uniforms are
handled: neccessary uniforms are selected and applied when program is
applied.
I think shaders could be selected and compiled in the same moment ie when
program is applied and using similar logic and handling as uniforms. We
would need to have the functional name for the shader to select shaders used
by program. That name would work bit like uniform name. It was "semantics"
parameter in VirtualProgram but some other shader names could be used as
well for this purpose.
And the other subject I think may affect your work are Open GL 4.0
subroutines. Lets make the shader composition in OSG future compatible with
this concept.
That are only my 2 cents. I don't want to start any fierce discussion. I
will accept a solution you would select as most appropriate.
Cheers,
Wojtek
--------------------------------------------------
From: "Robert Osfield" <robert.osfi...@gmail.com>
Sent: Monday, June 21, 2010 7:02 PM
To: <osg-submissi...@lists.openscenegraph.org>
Subject: Re: [osg-submissions] Shader composition
Hi Roland, Johannes et. al,
I've mostly cleared my desk for other tasks so am now ready to dive
back into the topic of shader composition. My plan this week is to
dig out my own design notes, and do a review of Roland's submissions
and experiment with the runtime usage/results of the submission to get
better idea of the problem domain and the submission itself.
Any updates on the submission or any thoughts on shader composition
would be most welcome. Once I'm more back up to speed on Roland's
submission and my collected more of my own thoughts together I'll
strik a discussion on osg-users about shader composition, but feel
free to chip in on this thread if you have comments about Roland's
submission.
Cheers,
Robert.
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